Outcome measure
Major injury was assessed with the question, “In the past two years, have you sustained any
major injury?” (Yes/No) “What was the cause of that injury? [Multiple answers are allowed]” (“Traffic accident, Struck by person or object, c. Fire, flames, burn, electric Shock, Drowning, Poisoning, Animal attack or bite, Fall, and Others”). [18] We grouped these injury causes into 1) road traffic injuries, 2) fall injuries, and 3) other injury.
Sociodemographic information included age (years), sex (male, female), education (none, < 5 years, 5–9 years, and ≥ 10 years), Cast or tribe (Scheduled tribe, Scheduled caste, other backward classes, none of these), residence (rural, urban) and subjective socioeconomic status. The latter was sourced from the item, “Please imagine a ten-step ladder, where at the bottom are the people who are the worst off – who have the least money, least education, and the worst jobs or no jobs, and at the top of the ladder are the people who are the best off – those who have the most money, most education, and best jobs. Please indicate the number given (1–10) on the rung on the ladder where you would place yourself.” [18]. Socioeconomic steps 1 to 3 were classified as poor, 4–5 as medium, and 5–10 as high socioeconomic status.
Sleep problems were assessed with four questions: (1) “How often do you have trouble falling asleep?” (2) “How often do you have trouble with waking up during the night?” (3) “How often do you have trouble with waking up too early and not being able to fall asleep again?” (4) “How often do you feel really rested when you wake up in the morning?” Responses options were “never, rarely (1–2 nights per week), occasionally (3–4 nights per week), and frequently (5 or more nights per week)” [18]. Sleep problems were coded as “frequently” for the first three symptoms and “never or rarely” for the fourth symptom as one. Participants who reported any of these four symptoms were classified as having sleep problems [19].
Depressive symptoms were assessed with a modified Centre for Epidemiological Studies Depression Scale (CES-D-10) [20]. The 10 items included seven negative symptoms (trouble concentrating, feeling depressed, low energy, fear of something, feeling alone, bothered by things, and everything is an effort), and three positive symptoms (feeling happy, hopeful, and satisfied). Response options included rarely or never (< 1 day), sometimes (1 or 2 days), often (3 or 4 days), and most or all of the time (5–7 days) in a week prior to the interview. For negative symptoms, rarely or never (< 1 day), and sometimes (1 or 2 days) were scored zero, and often (3 or 4 days) and most or all of the time (5–7 days) categories were scored one. Scoring was reversed for positive symptoms. The overall score ranges from zero to 10 and scores of four or more were indicative for depressive symptoms [21]. The Cronbach α of the CES-D-10 in this study was 0.79.
Chronic conditions were assessed with the question, “Has any health professional ever told you that you have…?”: 1) “ Hypertension or high blood pressure (Yes/No); 2) Diabetes or high blood sugar; 3) Cancer or malignant tumor; 4) Chronic lung disease such as asthma, chronic obstructive pulmonary disease/Chronic bronchitis or other chronic lung problems; 5) Chronic heart diseases such as Coronary heart disease (heart attack or Myocardial Infarction), congestive heart failure, or other chronic heart problems; 6) Stroke; 7) Arthritis or rheumatism, Osteoporosis or other bone/joint diseases; 8) Any neurological, or psychiatric problems such as depression, Alzheimer’s/Dementia, unipolar/bipolar disorders, convulsions, Parkinson’s etc.; and 9) High cholesterol (Yes/No).” [18]. Responses for the nine chronic conditions were summed and trichotomized into 0,1, or ≥ 2 chronic conditions.
Functional disability was sourced from Activities of Daily Living (ADL) (6 items) and Instrumental Activities of Daily Living (IADL) (7 items) [22, 23]. Cronbach alpha for the ADL and IADL scale was 0.89. Responses were “Yes/No” and were trichonomized into 0,1, or ≥ 2 ADL/IADL items.
Hand grip strength (HGS) was measured with a “Baseline Smedley Spring type dynamometer” on “each hand twice, beginning with the dominant hand, alternating hands in between measurements” [18]. A mean HGS (kg) variable was calculated from all four measurements [24]. HGS < 30 kg for men, < 20 kg for women using the average value of the four handgrip assessments were defined as “weak” [25].
Symptom-based pain was defined as troubled by pain and required some form of medication or treatment for relief of pain [18].
Anthropometry: “Height and weight of adults were measured using the Seca 803 digital scale.” [18]. “BMI was calculated according to Asian criteria: underweight (< 18.5 kg/m2), normal weight (18.5–22.9 kg/m2), overweight (23.0-24.9 kg/m2), class I obesity (25.0-29.9 kg/m2), and class II obesity (≥ 30.0 kg/m2)” [26].
Binge drinking was assessed with the question, “In the last 3 months, how frequently on average, have you had at least 5 or more drinks on one occasion?” [18] and defined as “one to three days per month, one to four days per week, five or more days per week, or daily.”
Current tobacco use was sourced from two items, 1) “Do you currently smoke any tobacco products (cigarettes, bidis, cigars, hookah,cheroot, etc.)? and 2) Do you use smokeless tobacco (such as chewing tobacco, gutka, pan masala, etc.)?” [18].
Vigorous physical activity. “ For vigorous activity, respondents were asked about their involvement in running or jogging, swimming, going to a health centre/gym, cycling, digging with a spade or shovel, heavy lifting, chopping, farm work, fast bicycling, and cycling with loads.” [18]. Participants, who more than once a week engaged in vigorous physical activity were defined as sufficient physical activity [27].
Vision was assessed with two questions, 1) “How good is your eyesight for seeing things at a distance, like recognizing a person across the street (or 20 meters away), whether or not you wear glasses, contacts, or corrective lenses?” And 2) “ How good is your eyesight for seeing things up close, like reading an ordinary newspaper print whether or not you wear glasses, contacts, or corrective lenses?” [18]. Response options ranged from 1. Very good to 5. Very poor and poor near or far vision as defined as “poor or very poor”
Cognitive functioning measures in the LASI were derived from the cognition module of the Health and Retirement Study (HRS), including memory (immediate and delayed word recall), orientation (time and place), arithmetic function (backward counting, serial 7, computation), executive function (paper folding and Pentagon drawing), and object naming. A composite cognitive index is created with the lowest 10th percentile as a proxy measure of poor cognitive functioning [18].
Hearing problem was measured with the item. “Have you ever been diagnosed with any hearing or ear-related problem or condition?” (Yes/No) [18].
Inadequate balance was defined as < 10 seconds or no attempt [18].
Data analysis